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From cf712371da839a8655506aacc2908f7ffc3988ab Mon Sep 17 00:00:00 2001
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From: jmaloy <jmaloy@redhat.com>
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Date: Thu, 13 Feb 2020 21:08:17 +0100
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Subject: [PATCH 1/6] util: add slirp_fmt() helpers
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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Message-id: <20200213210818.9090-2-jmaloy@redhat.com>
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Patchwork-id: 93831
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O-Subject: [RHEL-7.8 qemu-kvm PATCH 1/2] util: add slirp_fmt() helpers
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Bugzilla: 1800515
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RH-Acked-by: Maxim Levitsky <mlevitsk@redhat.com>
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RH-Acked-by: Eduardo Habkost <ehabkost@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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From: Marc-André Lureau <marcandre.lureau@redhat.com>
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Various calls to snprintf() in libslirp assume that snprintf() returns
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"only" the number of bytes written (excluding terminating NUL).
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https://pubs.opengroup.org/onlinepubs/9699919799/functions/snprintf.html#tag_16_159_04
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"Upon successful completion, the snprintf() function shall return the
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number of bytes that would be written to s had n been sufficiently
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large excluding the terminating null byte."
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Introduce slirp_fmt() that handles several pathological cases the
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way libslirp usually expect:
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- treat error as fatal (instead of silently returning -1)
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- fmt0() will always \0 end
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- return the number of bytes actually written (instead of what would
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  have been written, which would usually result in OOB later), including
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  the ending \0 for fmt0()
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- warn if truncation happened (instead of ignoring)
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  Other less common cases can still be handled with strcpy/snprintf() etc.
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Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
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Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
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Message-Id: <20200127092414.169796-2-marcandre.lureau@redhat.com>
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Manually re-adapted from 30648c03b27fb8d9611b723184216cd3174b6775
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since cerry-pick cannot be used here. There is no util.c file in this
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code version, so we add the two new functions as static functions in
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the file where they are going to be used.
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Signed-off-by: Jon Maloy <jmaloy@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 slirp/tcp_subr.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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 1 file changed, 65 insertions(+)
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diff --git a/slirp/tcp_subr.c b/slirp/tcp_subr.c
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index 19e2245..e83575e 100644
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--- a/slirp/tcp_subr.c
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+++ b/slirp/tcp_subr.c
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@@ -44,6 +44,9 @@
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 /* Don't do rfc1323 performance enhancements */
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 #define TCP_DO_RFC1323 0
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+static int slirp_fmt(char *str, size_t size, const char *format, ...);
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+static int slirp_fmt0(char *str, size_t size, const char *format, ...);
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+
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 /*
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  * Tcp initialization
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  */
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@@ -935,3 +938,65 @@ int tcp_ctl(struct socket *so)
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     sb->sb_wptr += sb->sb_cc;
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     return 0;
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 }
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+
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+static int slirp_vsnprintf(char *str, size_t size,
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+                           const char *format, va_list args)
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+{
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+    int rv = vsnprintf(str, size, format, args);
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+
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+    if (rv < 0) {
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+        g_error("vsnprintf() failed: %s", g_strerror(errno));
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+    }
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+
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+    return rv;
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+}
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+
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+/*
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+ * A snprintf()-like function that:
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+ * - returns the number of bytes written (excluding optional \0-ending)
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+ * - dies on error
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+ * - warn on truncation
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+ */
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+static int slirp_fmt(char *str, size_t size, const char *format, ...)
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+{
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+    va_list args;
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+    int rv;
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+
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+    va_start(args, format);
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+    rv = slirp_vsnprintf(str, size, format, args);
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+    va_end(args);
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+
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+    if (rv > size) {
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+        g_critical("vsnprintf() truncation");
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+    }
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+
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+    return MIN(rv, size);
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+}
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+
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+/*
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+ * A snprintf()-like function that:
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+ * - always \0-end (unless size == 0)
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+ * - returns the number of bytes actually written, including \0 ending
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+ * - dies on error
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+ * - warn on truncation
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+ */
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+static int slirp_fmt0(char *str, size_t size, const char *format, ...)
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+{
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+    va_list args;
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+    int rv;
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+
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+    va_start(args, format);
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+    rv = slirp_vsnprintf(str, size, format, args);
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+    va_end(args);
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+
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+    if (rv >= size) {
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+        g_critical("vsnprintf() truncation");
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+        if (size > 0)
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+            str[size - 1] = '\0';
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+        rv = size;
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+    } else {
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+        rv += 1; /* include \0 */
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+    }
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+
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+    return rv;
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+}
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-- 
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1.8.3.1
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